As a technique to carry a wafer by a fluid current, there is disclosed in Japanese Patent Publication Laid Open No. 38828-1980 such that a groove is formed on the surface of an orbit and by injecting fluid along the groove, a vacuum condition is created when the fluid is sucked into the groove from a thin film of fluid.
This technique is excellent in its performance when it is applied to a carrying mechanism.
However, the inventors have found various following problems when the aforementioned carrying device is put into practical use.
First, it is difficult to maintain a wafer in a stationary condition at a predetermined position. For example, in the case where the wafer is introduced into a film forming chamber, it is desired that the discrepancy of the stationary position of the wafer from a predetermined position is in a range of .+-.0.2 mm.
Therefore, it is necessary to guide the wafer to a predetermined position with an accuracy of .+-.0.2 mm. Next, it is necessary to make the wafer stand still at the position without causing vibration in the wafer.
The inventors attempted to make the wafer stand still with the accuracy in accordance with the aforementioned conventional technique, however, it was difficult to maintain the wafer in a stationary condition with such accuracy. Further, there were no carrying devices capable of making the wafer stand still with the aforementioned accuracy.
After all, according to the conventional carrying device, vibrations were caused in the radial, circumferential and horizontal directions when the wafer was in a stationary condition, and the amplitude of the vibration far exceeded 0.2 mm.
Secondarily, it was found that the predetermined characteristics of the wafer could not be necessarily obtained in the case where the wafer was carried with the conventional carrying device and subjected to processing such as film forming or etching. For example, when an oxide film was formed on the wafer, its insulating property was not good, and when the wafer was subjected to etching, an etching with high selectivity could not be performed. As a result of investigations made by the inventors to ascertain its cause, it was found that impurities such as particles and moisture were deposited on the surface of the wafer deteriorating the processability. As a result of further various investigations, it was found that such impurities had been deposited on the wafer while the wafer was being carried. Especially, it was found that particles had been remarkably generated.
The aforementioned problems have not been known until now, being found by the inventors for the first time.